Diffusion-weighted imaging based on apparent diffusion coefficient (ADC) has been used for bladder urothelial carcinoma grading. However, a considerable overlap between the low- and high-grade bladder urothelial carcinoma has hindered its clinical acceptance. We employed high b-value diffusion imaging with a non-Gaussian fractional-order calculus (FROC) diffusion model for grading bladder urothelial carcinoma. Significant differences were observed in the FROC parameters D, β and μ, between the low- and high-grade urothelial carcinoma. The combination of the FROC parameters provided substantially better performance than ADC. These findings indicate a promising role of FROC parameters for characterizing bladder urothelial carcinoma and beyond.